python - 验证集合时调用的方法

Question

假设我有一个列表Q。在下面的代码中:

while Q:
    do_something()
    Q.pop()

在while Q语句中，调用了列表Q的什么方法？是__len__方法吗？

Answer 1

在 Python 3.x 中，它是 __bool__或__len__:

object.__bool__(self)

Called to implement truth value testing and the built-in operation bool(); should return False or True. When this method is not defined, __len__() is called, if it is defined, and the object is considered true if its result is nonzero. If a class defines neither __len__() nor __bool__(), all its instances are considered true.

在 2.x 中它被命名为 __nonzero__ ;请参阅what's new in 3.0 .